Nitric oxide complexes in myocardial tissues from GSNO-treated rat hearts were studied using electron paramagnetic resonance (EPR) spectroscopy. Nitric oxide complexes of myoglobin, hemoglobin, and cytochrome c systems studied. S-band spectra have been obtained showing improved resolution of hyperfine structure. Experiments are now being conducted to exploit the use of multiquantum EPR to study these complexes.